1. Field of the Invention
The present invention relates to a steering damper control apparatus that controls a damping force of a steering damper provided in a steering mechanism of a vehicle to adjust a steering damping force, and to a saddle riding type vehicle including the same.
2. Description of the Related Art
Recently, saddle riding type vehicles including a steering damper control apparatus to adjust a damping force of a steering mechanism in order to stabilize posture changes and to ease the riders' burden have been increasing in popularity. Such steering damper control apparatus include the following.
A first apparatus of this type has a steering mechanism, a steering damper, an adjusting mechanism, a rear stroke sensor, and a control device (see Japanese Unexamined Patent Publication No. 2009-126432, for example). The steering mechanism is pivotably supported by a vehicle body. The steering damper applies a damping force to the torque of the steering mechanism. The adjusting mechanism adjusts the damping force of the steering damper. The rear stroke sensor detects an amount of stroke of a rear suspension. Based on outputs of the rear stroke sensor, the control device, when the vehicle is slowing down, controls the adjusting mechanism to increase the damping force of the steering damper compared with a time of steady traveling.
This first apparatus, when the vehicle is determined to be slowing down based on the outputs of the rear stroke sensor, increases the damping force of the steering damper. This can prevent kickbacks produced against the rider's intention by the steering mechanism undergoing disturbance of the traveling surface, for example. As a result, posture changes of the vehicle can be prevented even when the vehicle is slowing down.
A second apparatus of this type includes a steering damper which adjusts a damping force according to an amount of operation of the accelerator. When an opening degree of the accelerator is small, the vehicle is determined to be traveling at low speed, and the damping force is kept low. When the opening degree of the accelerator is large, the vehicle is determined to be traveling at high speed, and the damping force is increased (see Japanese Unexamined Patent Publication No. 2001-301682, for example).
This second apparatus determines a traveling state based on the amount of operation of the accelerator, thus preventing the steering from becoming unstable which would easily produce a situation where the front wheel is subject to levitation. As a result of this determination, posture changes of the vehicle can be prevented during acceleration.
A third apparatus of this type includes an acceleration detector and a control device (see Japanese Unexamined Patent Publication No. 2002-302085, for example). The acceleration detector detects acceleration of the vehicle body. Only when the acceleration exceeds a threshold value, the control device causes a steering damper to generate a damping force.
Although a load of the front wheel will decrease to produce a kickback easily when acceleration reaches or exceeds the threshold value, this third apparatus can increase the damping force of the steering damper to prevent a kickback. As a result, posture changes of the vehicle can be prevented during acceleration.
However, the above conventional examples with such constructions have the following problems.
When the rear wheel spins idly, the rear wheel may sway sideways relative to the front wheel, thus changing the posture of the vehicle to a large extent. This tends to occur when a coefficient of friction of the traveling surface is low, and during cornering on a rough surface such as those used by off-road vehicles, for example, in which case the drive of the rear wheel will greatly deviate from the traveling direction. When such a posture change occurs, the drive of the rear wheel will be unavailing to the traveling, and will become a very serious loss especially in race running or the like.
The first conventional apparatus noted above determines deceleration based on an amount of stroke of the rear suspension, and increases the damping force of the steering damper. However, since in the situation described above, there occurs also a situation in which the stroke of the rear suspension shortens, it cannot cope with the above situation.
The second apparatus determines acceleration based on the accelerator opening degree, and increases the damping force of the steering damper. However, since in the above situation the accelerator opening degree may be small, it may be unable to cope with the above situation also.
The third apparatus increases the damping force of the steering damper based on the acceleration of the acceleration detector having exceeded the threshold value. However, since acceleration can be close to zero in the above situation, it may be unable to cope.